1. Field of the Invention
The present invention relates to a method for controlling an overload of processors of a centralized and distributed operating hybrid full electronic switching system wherein a part of the functions of the system is processed in a distributed manner, while the other part of the functions is processed in a centralized manner.
2. Description of the Prior Art
Control for an overload is used to continuously provide a stable service while minimizing a failure of service under an overload condition of the processors through a determination about and a control for the overload. Conventional methods of controlling an overload in a switching system are classified into a method for determining the overload of the main processor and a method for controlling the overload of the main processor. As the method for determining the overload of the main processor, there have been known a method using a CPU occupancy rate, a method using a service queue of processors, a method using the number of services required in the processors. In the case of the method using the number of services, a determination that the overload of the main processor has occurred is made when the number of services is not less than a particular critical value. As the method for controlling the overload of the main processor, there have been known a method of determining a call service ratio between call services to be accepted and call services to be suppressed in a control interval, in accordance with the level of the overload, and a method of determining an interval of accepting all call services and an interval of suppressing all call services.
In the case of determining the overload using only the CPU occupancy rate, a determination that the overload has occurred may be made even if nothing interferes with the call processing service. This is because the CPU occupancy rate may be increased due to an operation maintenance software irrespective of the call processing traffic. The erroneous determination results in degradation of service quality.
In the cases of using the length of the service queue of each processor and the number of calls generated, an analysis of sufficient field operating data and a precisely simulated test are required to derive the critical value used for the determination about an overload. Furthermore, these methods have a disadvantage that the derived critical value should be varied depending on the type of call. The disadvantages encountered in the conventional methods of only utilizing the CPU occupancy rate, the service queue and the number of calls generated can be complemented by utilizing both the CPU occupancy rate and the monitoring for the execution delay of the processor.
In the method of controlling the overload, wherein new calls at a next interval are totally suppressed when the CPU occupancy rate is not less than the particular critical value and totally accepted when the CPU occupancy rate is less than the critical value, the control for the overload may be excessive because of an increased width between the increase in service and the decrease in service. On the other hand, the control method wherein the suppression rate is increased as the level of the overload increases has a possibility that an initial control may be failed when an overload occurs due to an abrupt increase in load.